In order to regulate the water pH level in recirculating aquaculture system (RAS), a CO2 removal device was designed based on gas exchange principle and tested, in the wish to remove CO2 from aquaculture water and adjust the pH drop caused by CO2 accumulation, so that the cultured fish would live in a suitable pH environment. During the test, water temperature was controlled at (25 ± 0.5) °C, pH was measured every hour, and alkalinity was measured every 4 hours; water samples were taken from barrels culturing fish and were filtered with 40um syringe filter before detection; the experimental cycle was 24 h. The results showed that the installation of the CO2 removal device in RAS could effectively remove CO2 in the water body and stabilize the water pH level within a suitable range between 7.39 - 7.42; the CO2 concentration exhibited a decreasing trend, and after 24 h it reached 7-8 mg/L from the initial 13.16mg/L, decreased by nearly 50%; while in the recirculating water system without the CO2 removal device, CO2 content continued to increase and reached 37 mg/L after 24 h, meanwhile the pH level continued to decrease and finally to 6.72~6.81. The research shows that the CO2 removal device can effectively remove CO2 in the water of RAS and maintain the pH level at a suitable range for fish growth.